I am glad someone finally said this, as after I read a few explanations, I could see that the temperature reading would be off somewhat, especially in the resolution used.
Thanks, Will *********** REPLY SEPARATOR *********** On 5/28/2011 at 11:53 AM Tom Van Baak wrote: >The problem is actually with all three parts: the 1620 sensor, TBolt >firmware, and with Heather. Let me explain. > >1) While the root cause is an anomaly in the DS1620 chip, Dallas >identified (not solved) it and described a work-around after Weather >Station users noticed glitches in the late 90's. > >2) The next problem is Trimble did not implement the recommended >software fix in their TBolt firmware. Worse yet, Trimble computes a >running average temperature and returns this as "the temperature" >instead of the actual instantaneous 1620 reading. Further they use >24-bit floating point precision in the TSIP packet. Side effects: >a) the returned temperature is biased and late due to the LPF, >b) users can mistake filtered floating point for mK or uK resolution, >c) any 1620 glitches are "smoothed" instead of handled as Dallas >suggested, and d) internal disciplining algorithms may use the bad >temperature values as input. > >3) The final issue is that LH displays the filtered TSIP temperature >rather than the actual 1620 temperature reading. Thus you often >see exponential curves in temperature plots instead of true steps. >And glitches too. > >Anyway, since we can't change the 1620 design; and we can't >change the TBolt firmware, the solution for Alberto (and anyone >else) is for LH to report the correct temperature. > >Mark -- the trick is to recreate the raw quantized 1620 temperature >from the TSIP averaged temperature readings and then implement >the 1620 glitch fix per the Dallas memo. This way the readings are >on-time, reflect the actual ~1/140th C quantization of the chip, and >have no glitches. The difference is dramatic. > >To de-average see at unavg.c in www.leapsecond/tools/ > >To de-glitch see the Dallas memo 2000-ds1820-report.pdf under >www.leapsecond.com/pages/tbolt-1620/ > >/tvb > > >_______________________________________________ >time-nuts mailing list -- time-nuts@febo.com >To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >and follow the instructions there. > >__________ Information from ESET Smart Security, version of virus signature database 5851 (20110206) __________ > >The message was checked by ESET Smart Security. > >http://www.eset.com _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.